-1. Rock, roll and twist again?

Percussion instruments are three dimensional objects, so in order to effectively describe what I am looking at when I see design problems, below is a diagram of the three axis on which measurements are made.

The X direction of movement is forwards and backwards. The Y direction is left and right. The Z direction is up and down.

However musical instruments don’t just exist on paper, they are used in the real world, and thus are subjected to forces that are also three dimensional.

These forces are called Roll, Pitch and Yaw. They are measured in degrees around their respective axis, and I have colour coded them for clarity. For example, Roll (in green) occurs when an instrument wobbles front to back, it is measured in around the Z axis. Pitch is one that wobbles side to side. Yaw is an instrument that has a note bed that rotates when viewed from directly above. In this post I am looking at roll.

Paul the Porter, and Preschool Paul are going down to the park. As they approach the see saw, they notice that it is balanced horizontally on its base.

Preschool Paul loves the see saw, he knows all about how, when on side goes up, the other side goes down because it is only fixed in the middle. Now imagine that the see saw is the low end of an instrument; as the naturals go down, the accidentals go up. This is roll.

Oops! And here it is, our first example of bad design – a Bergerault Pedal Glock with a central leg at either end. Just like the see saw above! Now glockenspiels may not be very wide at the low end, but they are wide enough, and certainly heavy enough for this central leg to be a weak link in the design. Consider also that it is a “pedal” glock, so there is the additional problem of moving parts within the damping mechanism that need to operate efficiently. In my professional opinion I give this instrument no chance of surviving for the long term.

Even Preschool Paul knows that standing on one leg is a recipe for disaster. Instead he stands with his legs spread wide whilst holding his heavy school bag above his head.

Now this as we all know is solid and stable, and on paper looks like the perfect solution to roll. However, if Preschool Paul removes his shoes and stands on a polished floor…

With socks sliding along a polished floor, his feet slide apart. Substitute the feet for wheels, and make the centre of the X the weakest part…

Oh look, we have an Adams marimba using a design that is featured on just about every one of their instruments. A design that is fundamentally floored in concept and the end result is hundreds of instruments all over the place that suffer from dreadful roll issues. What is more, because the same components are used on all of their instruments, the bigger the instrument, the bigger the problem.

Bergerault use a capital I as the basis of their design – I for inadequate. Adams use an X for exceptionally bad. Any instrument design that transfers the weight of an instrument directly through its centre line is always going to be exceptionally bad and the resultant instrument is going to be inadequate to withstand the forces applied.

So what is the solution to preventing roll? For me, simple is best, and the simplest solution is a square. The only decision is either solid or hollow.

The problem with a solid end, like the Deagan Arora (above) is weight, so I mainly go with a hollow square, ie, two legs, the bottom transom with the casters attached, and the top defined by the note bed. In order to maximise stability, I make the legs as wide as possible, even splaying the legs out at the narrow end to make a trapezium.

In the next part of this series I will look at pitch, which is when the instrument rocks from side to side.